AP Bio Unit 2

Which of the following statements best predicts the effect of increasing the permeability of the mitochondrial membranes to large molecules? A ATP production will increase because of an increase in the rate at which proteins diffuse out of mitochondria. B ATP production will increase because of an increase in the mixing of mitochondrial and cytosolic substances. C ATP production will decrease because of an increase in the occurrence of uncontrolled chemical reactions. D ATP production will decrease because of an increase in the surface area of the mitochondrial membranes.

ATP production will decrease because of an increase in the occurrence of uncontrolled chemical reactions. *Answer C* Correct. ATPATP production will most likely decrease. Increasing the permeability of the mitochondrial membranes to large molecules will likely result in a variety of uncontrolled substrate-enzyme interactions that will disrupt normal mitochondrial function.

Which of the following best describes the numbered areas? A Areas 1 and 3 are polar, since the membrane molecules are aligned with water molecules. B Area 2 is polar, since water has been excluded from this area of the membrane. C Areas 1 and 3 are hydrophilic, since membrane molecules formed covalent bonds with water. D Area 2 is nonpolar, since hydrogen bonds between the adjacent lipids hold the membrane together.

Answer A Correct. As indicated in the diagram, the heads of the phospholipids in areas 1 and 3 are adjacent to water molecules, which shows that the phospholipid heads are hydrophilic.

Which of the following best predicts the effect of not having ATP available to supply energy to this process? A H+ ions will stop moving through the protein. B H+ ions will move in the other direction through the protein. C H+ ions will continue to move through the protein in the original direction but at a slower rate. D H+ ions will begin to move through the phospholipid portion of the membrane in the original direction.

Answer A Correct. Metabolic energy such as ATPATP is required for active transport of ions against a concentration gradient.

Of the two cells represented in the figure, which would likely be more efficient at exchanging substances with the surrounding environment? A Cell A, because it has the larger surface-area-to-volume ratio. B Cell A, because it has the smaller surface-area-to-volume ratio. C Cell B, because it has the larger surface-area-to-volume ratio. D Cell B, because it has the smaller surface-area-to-volume ratio.

Answer A Correct. Of the two cells represented in the figure, Cell A has the larger surface-area-to-volume ratio of 0.91 compared to a surface-area-to-volume ratio of 0.75 for Cell B. Cell A would likely exchange substances with the surrounding environment at a greater rate.

A team of biologists develop a new drug, and one team member hypothesizes that the drug is incapable of freely passing across the plasma membrane and requires the help of membrane proteins to enter cells. Alternatively, another biologist on the team hypothesizes that the drug can diffuse passively across the plasma membrane like O2 and CO2 can. Which of the following, if true about the drug, best supports the alternative hypothesis that the new drug will exhibit simple diffusion across plasma membranes? A The drug is a small nonpolar molecule. B The drug is a small charged molecule. C The drug is a large polar molecule. D The drug is a large charged molecule.

Answer A Correct. Small nonpolar molecules freely pass across the plasma membrane. If the drug is a small nonpolar molecule, this supports the alternative hypothesis.

A model of the plasma membrane showing several biological molecules, including a transmembrane protein, is shown in Figure 1. Which statement best explains why correct protein folding is critical in the transmembrane protein shown above? A Interactions of the hydrophobic and hydrophilic amino acids help to anchor the protein in the membrane. B Interactions of the peptide bonds of the protein with the membrane will affect the rate at which substances can cross the membrane. C Interactions of the protein and phospholipids increase membrane fluidity. D Interactions of the quaternary structure of the protein will increase hydrogen bonding in the membrane and make the membrane less fluid.

Answer A Correct. Tertiary structure of the protein resulting from hydrophobic and hydrophilic interactions plays a key role in how the protein interacts with the hydrophobic tails and hydrophilic head of the membrane phospholipids.

Muscle cells have high ATP demands. Which of the following is a scientific claim about how the structure of the mitochondria in muscle cells should be different than it is in other cells because of the high energy demands of mitochondria? A The inner membrane of the mitochondria in muscle cells should have more folds to increase the surface area, allowing more ATPATP to be synthesized. B The inner membrane of the mitochondria in muscle cells should be more permeable to large enzymes, allowing the same reactions to occur in both compartments of the mitochondria. C The outer membrane of the mitochondria in muscle cells should be thicker, allowing more rapid diffusion of molecules into the mitochondria. D The outer membrane of the mitochondria of muscle cells should have more folds, increasing the surface area for faster diffusion of molecules from the cytoplasm.

Answer A Correct. The amount of ATPATP produced is related to the number of ATPATP synthase molecules located on the inner mitochondria membrane. Increasing the folds increases the number of ATPATP generation sites and results in more ATPATP production.

Researchers propose a model to explain variation in phytoplankton cell sizes in a marine environment. They base their model on the idea that smaller cells absorb nutrients more efficiently. The researchers predict that the mean diameter of phytoplankton cells will change by 50 micrometers for every 5-kilometer increase in distance from the shore because of a gradual decrease in nutrient availability. To test their model, the researchers determine that the phytoplankton cells found closest to shore have a mean diameter of 900 micrometers. Based on the model, what will be the mean diameter of the phytoplankton cells that are found 25 kilometers from shore? A 650 micrometers B 875 micrometers C 925 micrometers D 1150 micrometers

Answer A Correct. The model predicts that phytoplankton cell size will decrease with increasing distance from the shore, resulting in increased efficiency of nutrient absorption. The correct value was arrived at by subtracting 250 from 900.

Which of the following claims is scientifically accurate and consistent with an observation that a decrease in lysosome production within a cell leads to a decline in mitochondrial activity? A A lack of lysosomes will cause a decrease in the synthesis of enzymes necessary for cellular respiration. B Fewer lysosomes will be available to break down macromolecules to provide the necessary nutrients for cellular respiration. C Fewer lysosomes will be available to store materials required for the functioning of the mitochondria. D Lysosomes will not be available to modify proteins so that they are targeted to the mitochondria.

Answer B Correct. A function of the lysosomes is the breakdown and recycling of macronutrients, such as carbohydrates. Products of carbohydrate breakdown such as glucose are utilized by the mitochondria in the process of cell respiration.

Plant cell walls are composed of cellulose, while fungal cell walls are composed of chitin. A group of scientists hypothesize that this difference means the cell wall has largely different functions in plant cells and fungal cells. Alternatively, another group of scientists hypothesize that despite their biochemical differences, plant and fungal cell walls serve similar functions. Which of the following observations would best support the alternative hypothesis described above? A Plant cell walls are found just outside the plasma membrane, while fungal cell walls are found just beneath the plasma membrane. B In both plant cells and fungal cells, the cell wall surrounds the outside of the cell membrane. C Some plant cells have secondary cell walls that confer additional rigidity, while fungal cells do not. D Photosynthesis occurs in plant cells, but it does not occur in fungal cells.

Answer B Correct. In both plants and fungi, a major function of the cell wall is to confer structural rigidity to the cell. Thus, in both cell types, the cell wall's location is similar. This is evidence supporting the alternative hypothesis proposed above.

Which of the following statements best explains the processes of passive and active transport? A Passive transport is the net movement of substances down a concentration gradient that requires metabolic energy. Active transport is the movement of substances up a concentration gradient that does not require energy. B Passive transport is the net movement of substances down a concentration gradient that does not require metabolic energy. Active transport is the movement of substances up a concentration gradient that requires energy. C Passive transport is the net movement of substances up a concentration gradient that requires metabolic energy. Active transport is the movement of substances down a concentration gradient that does not require metabolic energy. D Passive transport is the net movement of substances up a concentration gradient that does not require metabolic energy. Active transport is the movement of substances down a concentration gradient that requires energy.

Answer B Correct. Passive transport is the net movement of substances down (with) a concentration gradient that does not require metabolic energy and active transport is the movement of substances up (against) a concentration gradient that requires energy.

Which statement best describes the effect on water transport across the cell membrane if the aquaporin in the figure ceases to function? A Water molecules will no longer be able to move across the cell membrane. B Water molecules will still be able to move across the cell membrane but at a slower rate. C Water molecules will only be able to enter the cell by active transport. D Water molecules will move across the cell membrane at a faster rate without the aquaporin regulating their flow.

Answer B Correct. The aquaporin facilitates water passage, but water can still move across the membrane by osmosis.

Cholesterol is an important component of animal cell membranes. Cholesterol molecules are often delivered to body cells by the blood, which transports the molecules in the form of cholesterol-protein complexes. The complexes must be moved into the body cells before the cholesterol molecules can be incorporated into the phospholipid bilayers of cell membranes. Based on the information presented, which of the following is the most likely explanation for a buildup of cholesterol molecules in the blood of an animal? A The animal's body cells are defective in exocytosis. B The animal's body cells are defective in endocytosis. C The animal's body cells are defective in cholesterol synthesis. D The animal's body cells are defective in phospholipid synthesis.

Answer B Correct. The cholesterol-protein complexes are most likely moved into the body cells by endocytosis. A defect in endocytosis is likely to result in a buildup of cholesterol in the blood

The model below shows the structure of a portion of a plasma membrane in an animal cell. Which statement best explains the orientation of the phospholipid molecules in this model? A The nonpolar portions of the phospholipid molecules are attracted to the internal and external environments. B The hydrophilic phosphate groups of the phospholipid molecules are attracted to the aqueous internal and external environments. C The embedded proteins attract the fatty acid tails of the phospholipids, so the tails point away from the internal and external aqueous environments. D The fatty acid tails of the phospholipid molecules are hydrophilic and are repelled by the internal and external aqueous environments.

Answer B Correct. The hydrophilic polar phosphate groups of the phospholipid molecules orient toward the polar internal and external aqueous environments, forming a bilayer that keeps the hydrophobic portions of the phospholipids away from the polar molecules.

A cell's membrane potential is maintained by the movement of ions into and out of the cell. A model showing the influence of membrane proteins on the movement of sodium (Na+) and potassium (K+) ions across the plasma membrane is presented in Figure 1. Based on the model presented in Figure 1, which of the following outcomes will most likely result from a loss of protein X function? A The membrane potential will be disrupted by an increase in Na+ concentration inside the cell. B The membrane potential will be disrupted by an increase in K+K+ concentration inside the cell. C The membrane potential will be maintained by the Na+−K+Na+⁢−⁢K+ pump moving more K+ ions into the cell. D The membrane potential will be maintained by the diffusion of Na+ ions into the cell.

Answer B Correct. The intracellular K+ concentration will increase because the Na+−K+Na+−K+ pump will continue to transport K+ into the cell without any diffusing out of the cell. As a result, the cell's membrane potential will be disrupted.

Figure 1 shows a model of how a channel protein influences the movement of a particle across a cell's plasma membrane. Figure 1. A section of a cell's plasma membrane, showing a channel protein and a concentration gradient across the membrane An investigator wants to understand whether a newly found membrane protein is involved in membrane transport of a certain particle. Which investigation will help determine whether the new membrane protein is a channel protein involved in membrane transport? A Add small nonpolar molecules to the extracellular space and measure the direction of particle movement of the molecules. B Measure the rate of extracellular fluid movement into the intracellular space. C Add more of the proteins to the plasma membrane and measure the rate of the particle movement. D Remove ATP from the intracellular space and measure the rate of the particle movement into the intracellular space.

Answer C Correct. If the movement of particles is mediated by the channel protein, then an increase in proteins in the cell membrane should influence the rate of particle movement across the membrane.

Researchers have proposed a model of the process by which a newly synthesized protein is transported to the plasma membrane and secreted into the extracellular space. Based on the model, the newly synthesized protein is transported directly from the endoplasmic reticulum to which of the following? A The nucleus B The plasma membrane C The Golgi complex D The extracellular space

Answer C Correct. Membrane proteins and secreted proteins are synthesized by ribosomes bound to the surface of the endoplasmic reticulum. As shown in the figure, a newly synthesized secreted protein is transported by vesicles from the endoplasmic reticulum directly to the Golgi complex.

n an experiment, cells were isolated from an aquatic plant and suspended in pond water, a sucrose sugar solution, or distilled water. All of the cells were then viewed under a microscope. Compared with the cell in the pond water, the cell in the sugar solution appeared shriveled, and the cell in the distilled water appeared inflated. The results of the experiment are represented in Figure 1. Which of the following statements best explains the observations represented in Figure 1? A There was a net movement of sucrose out of the cell suspended in the sugar solution and a net movement of sucrose into the cell suspended in the distilled water. B There was a net movement of sucrose into the cell suspended in the sugar solution and a net movement of sucrose out of the cell suspended in the distilled water. C There was a net movement of water out of the cell suspended in the sugar solution and a net movement of water into the cell suspended in the distilled water. D There was a net movement of water into the cell suspended in the sugar solution and a net movement of water out of the cell suspended in the distilled water.

Answer C Correct. The plasma membrane that surrounds a living cell is typically permeable to water but not sucrose. In the experiment represented in Figure 1, there was a net movement of water out of the cell suspended in the sugar solution, causing the cell to appear shriveled, and a net movement of water into the cell suspended in the distilled water, causing the cell to appear inflated.

The transport of a substance across a plasma membrane of a specific organelle requires energy. The rate at which the transport takes place also depends on temperature. A scientist isolated the specific organelle and then used the following treatments to determine the conditions that will result in the maximal transport. All treatments contained the extracted organelle and were maintained at 25°C. The data from this experiment indicate that maximal rate of transport of protein X at 25°C occurs at an ATP concentration of 1.0μm/mL. Which procedure should be done next to gather data needed to meet the scientist's objective? A Incubate samples with the same four ATPATP concentrations at 30°C30°C. B Incubate samples containing 5.0μm/mL5.0μm/mL of ATPATP at four temperatures other than 25°C25°C. C Incubate samples containing 1.0μm/mL1.0μm/mL of ATPATP at four temperatures other than 25°C25°C. D Incubate samples containing 1.0μm/mL1.0μm/mL of ATPATP at 25°C25°C and determine the rate of transport for four other proteins.

Answer C Correct. This procedure combines the optimal ATPATP concentration for transport with data for transport rates at four other temperatures.

Aquaporins are channel proteins that facilitate the transport of water across the cell membrane. One group of researchers hypothesizes that without functional aquaporins, no water will be able to enter the cell. A different group proposes an alternative hypothesis, stating that even with nonfunctional aquaporins, a small amount of water will still cross the cell membrane. An experiment is set up in which plant cells with mutated (nonfunctional) aquaporins and plant cells with normally functioning aquaporins are both placed in distilled water. Which of the following data would support the alternative hypothesis? A Cells with functional aquaporins exhibit low turgor pressure and are hypertonic. B Cells with functional aquaporins exhibit high turgor pressure and are hypotonic. C Cells with mutated aquaporins exhibit an absence of turgor pressure and are completely plasmolyzed. D Cells with mutated aquaporins exhibit moderate turgor pressure and are hypertonic.

Answer D Correct. Even with mutated aquaporins, a small amount of water is able to enter and leave the cell. Thus, turgor pressure is not lost and the alternative hypothesis is supported.

Water is constantly diffusing into the cytosol of freshwater single-celled organisms. In order to maintain the proper solute concentrations in the cytosol, contractile vacuoles pump out the excess water. An experimenter placed single-celled organisms into various saline concentrations and recorded the ATP used by the contractile vacuole. The data are shown in the graph. Of the following, which additional investigation can be used to determine when the cells are in an isotonic solution? A Decreasing the salinity of the environment a little at a time until the ATP usage reaches a maximum B Decreasing the salinity of the environment a little at a time until ATP usage reaches a minimum C Increasing the salinity of the environment a little at a time until ATP usage reaches a maximum D Increasing the salinity of the environment a little at a time until the ATP usage reaches a minimum

Increasing the salinity of the environment a little at a time until the ATPATP usage reaches a minimum Answer D Correct. If the environment is isotonic to the cell, the net flow of water due to diffusion is zero, and ATPATP is not used to pump water out of the cell.

Changing the shape or morphology of the mitochondrial inner membrane can change the efficiency of mitochondrial function. Which of the following outcomes will most likely result from a change in the shape of the mitochondrial inner membrane from a highly folded surface to a smooth, flat surface? A Mitochondria will become more efficient because the inner mitochondrial membrane will become more permeable to ions. B Mitochondria will become more efficient because the total volume of the mitochondria will increase. C Mitochondria will become less efficient because the inner mitochondrial membrane will become less permeable to large molecules. D Mitochondria will become less efficient because the surface area of the inner mitochondrial membranes will decrease.

Mitochondria will become less efficient because the surface area of the inner mitochondrial membranes will decrease. *Answer D* Correct. The change to the inner mitochondrial membrane will result in a decrease in the membrane's surface area, which will reduce the efficiency of mitochondrial function because there will be less surface area for reactions to occur.

A spherical bacterial cell has a radius of 3μm. The human egg cell has a radius of 100μm. Which statement correctly indicates the cell that is able to more efficiently exchange materials with the external environment and provides a correct explanation? A The egg cell, because it has the smallest surface-to-volume ratio. B The egg cell, because it has the largest surface-to-volume ratio. C The bacterial cell, because it has the smallest surface-to-volume ratio. D The bacterial cell, because it has the largest surface-to-volume ratio.

The bacterial cell, because it has the largest surface-to-volume ratio. Answer D Correct. The bacterial cell is more efficient in the exchange of materials with the external environment. While the egg cell is much larger than the bacterial cell, the egg cell has a surface-to-volume ratio that is 33 times smaller than the bacterial cell's surface-to-volume ratio.

The figure shows a process by which a cell might absorb food from its surrounding environment and break it down for use as a source of energy and matter. The process involves lysosomes, which are membrane-bound organelles that contain hydrolytic enzymes. Activation of the hydrolytic enzymes requires an acidic pH, and lysosomes maintain an internal acidic pH by using ion pumps. Which of the following outcomes will most likely result from a loss of ion pump function in the cell's lysosomes? A The internal pH of the lysosomes will decrease, which will prevent the activation of hydrolytic enzymes and interfere with the intracellular digestion of food. B The internal pH of the lysosomes will increase, which will prevent the activation of hydrolytic enzymes and interfere with the intracellular digestion of food. C The internal pH of the lysosomes will decrease, which will activate hydrolytic enzymes and enhance the intracellular digestion of food. D The internal pH of the lysosomes will increase, which will activate hydrolytic enzymes and enhance the intracellular digestion of food.

The internal pH of the lysosomes will increase, which will prevent the activation of hydrolytic enzymes and interfere with the intracellular digestion of food. *Answer B* Correct. The lysosomes rely on the ion pumps to maintain an internal acidic pH. A loss of ion pump function will most likely result in an increase in the internal pH of lysosomes from acidic to neutral, which will prevent the activation of hydrolytic enzymes and interfere with intracellular digestion of food